Environmental impact
of ore smelting:
the African &
European experience
Vojtěch ETTLER
EGG – Environmental Geochemistry Group
Institute of Geochemistry,
Mineralogy and Mineral Resources
Faculty of Science,
Charles University in Prague
Albertov 6, 128 43 Prague 2,
Czech Republic
Number of colleagues and students:
Charles University in Prague
Martin Mihaljevič, Ondřej Šebek, Ladislav Strnad,
Jan Jehlička, Martina Vítková & many students
BRGM Orléans, France
Zdenek Johan, Patrice Piantone,…
Université d´Orléans, France
Jean-Claude Touray, Patrick Baillif,…
Czech Geological Survey
Bohdan Kříbek, František Veselovský, Vladimír Majer
People from Zambian & Namibian universities / geological surveys:
B. Mapani, F. Kamona, I. Nyambe, G. Schneider,…
Number of companies:
Kovohutě Příbram CZ (Pb smelter)
Zdeněk Kunický, Karel Vurm
Ongopolo Mines – Tsumeb smelter (Namibia)
Hans Nolte
Chambishi and Mufulira smelters (Zambia)
Tony Gonzáles and technical staff
Funding:
• Czech Science Foundation (GAČR 210/12/1413)
• Ministry of Education, Youth and Sports of the Czech Rep.
• Granting Agency of the AS CR and Charles University
• IGCP project No. 594 („Assessment of impact of mining and mineral
processing on the environment and human health in Africa“)
Background information
• non-ferrous metal smelting
• large amounts of smelting waste
• silicate slag
• fly ash – air polution control (APC) residues
• high concentrations of inorganic contaminants
• high leachability of metals and metalloids
• in EU classified as hazardous materials
• soil pollution by smelter emissions (fly ash)
Outline of the presentation
• Examples from Czech and African smelting sites
• Long-term environmental stability of waste
materials from the smelting activities (slags)
– insights from mineralogy/geochemistry
• Fate of smelter-derived contamination in the
environment (soils affected by smelter emissions)
Environmental stability
of smelting slags
Slags are silicate waste products resulting
from extraction of metals from ores by reducing
fusion. Slags contain high levels of contaminants.
Pb smelter
(Příbram, CZ)
• operating 200 years
• Pb-Ag production
• processing of ores
(1786-1974)
• processing of car
batteries since 1974
• 1.8 Mt of slags
on the dumps
Reducing fusion in shaft furnace
• temperature ~ 1350°C
• charge: Pb source (ore, Pb scrap), Fe scrap, calcite, Si source
• fuel (coal, coke)
Slag melt
tipped off >>>
Slag melt cooling
0.85-3.0 wt.% PbO
0.26-8.2 wt.% ZnO
up to hundreds ppm
As, Sb, Cu, Sn
slag
• 150-kg cone-shaped pots
• gravity separation during cooling
matte
metallic residue
Tsumeb smelting site (Namibia)
Tsumeb smelter (2007)
• ore mining/processing since 1907 (2 Mt Pb, 1 Mt Cu, 0.5 Mt Zn)
• 200 kt slags on the dumps
Ettler et al. (2009): Appl. Geochem. 24, 1.
Ettler et al. (2010): Comm. Geol. Survey Namibia 14, 3.
Nkana smelter (Kitwe, Zambia)
• in operation 1930-2009
• 20 Mt of Cu slag
• 1.8 wt.% Cu, 2.4 wt.% Co
• crushing to 15 mm
• reprocessing and Co recovery
Nkana old slag dumps
Chambishi smelter
(Zambia)
• electric arc furnace
• Co recovery (alloy 14% Co)
• 60-t glassy slag pots
• evacuated to dumps
<<< Pb slag dumps
Příbram, Czech Republic
Slag exposure to weathering
>>>
Tsumeb, Namibia
slag is milled and reused as a cover layer on mine tailing disposal site
Fine slag particle wind dispersal
20 μm
• slag crushers
• fine-grained slag particle dispersion in the environment (soils)
Kříbek et al. (2010): J. Geochem. Explor. 104, 69.
Slag mineralogy - solid speciation
• high-temperature
Ca-Fe alumosilicates
• spinel-family oxides
• silicate glass
• metallic fraction
Ol+Glass
Mel
melt enriched in metals
(18 wt.% Pb, 12 wt.% Zn,
12 wt.% Cu, 8 wt.% As)
Spl
Zn, Cu, Co enter into
the structures of silicates,
oxides and glass
Pb enters into the glass
Ettler et al. (2001): Can. Mineral. 39, 873.
Ettler et al. (2009): Appl. Geochem. 24, 1.
Vítková, Ettler et al. (2010): Mineral. Mag 74, 581.
Alteration products
Vítková, Ettler et al. (2010): Mineral. Mag. 74, 581.
Leaching experiments
• identification of dissolution and attenuation processes
• long-term simulations of waste/water interactions
• coupled to thermodynamic speciation-solubility modelling
• coupled to investigation of newly-formed phases
batch test
liquid-to-solid (L/S) ratio
Pb slag - long-term Pb leaching (batch)
Ettler et al. (2003): Mineral. Mag. 67, 1269.
Mineralogical controls
cerussite
PbCO3
20 µm
20 µm
cerussite
PbCO3
• XRD – SEM – TEM
• leached samples
• geochemical modelling
• natural weathering
HFO
20 μm
Ettler et al. (2003): Mineral. Mag. 67, 1269.
Pb slag - long-term Zn leaching (batch)
Ettler et al. (2003): Mineral. Mag. 67, 1269.
Tsumeb slag – batch leaching
Ettler et al. (2009): Appl. Geochem. 24, 1.
Natural alteration products
• bayldonite
Cu3Pb(AsO4)2(OH)2
• olivenite
Cu2AsO4OH
• lammerite
Cu3(AsO4)2
• lavendulan
NaCaCu5(AsO4)4Cl·5H2O
• hydrocerussite
Pb3(CO3)2(OH)
• litharge
PbO
Ettler et al. (2009): Appl. Geochem. 24, 1.
pH-static leaching experiments
pH-static leaching test
• paralel extractions at different pH values
• metal/metalloid leachability under various disposal scenarios
(dumping, stabilization, reuse)
Leaching behaviour
• not hazardous material according to EU limits
• potentially high release of Cu and Co in acidic environments
• dissolution of slag particles in soils (pH 4-5)
Vítková, Ettler et al. (2011): J. Hazard. Mater. 197, 417.
Conclusions #1
Environmental stability of slags
• understanding of metal-/metalloid-hosting phases
in slags is essential for subsequent determination
of possible environmental impacts
• natural alteration products are indicators of longterm weathering processes
• leaching experiments – accelerated weathering
>>> understanding and prediction of the chemical
processes
• slag crushing and milling facilities generate highly
reactive fine-grained dust
• high metal and metalloid release (mainly under low
pH conditions)
• formation of secondary alteration products can
lead to attenuation of contaminants
• highly soluble weathering products can be dissolved
during thunderstorm rain events
Fate of smelter-derived
contamination
in the environment
Soils in the vicinity of smelters are highly
polluted with metals/metalloids originating
from smelter stack emissions (fly ash).
• Pb emissions from the Příbram smelter, CZ
1969:
624 t Pb y-1
1999:
1.2 t Pb y-1
Pb migration in soil profiles
Depth (cm)
mobile Pb
FOREST SOIL
(700 m of the smelter)
Pb concentration (mg/kg)
• SEP and Pb isotopes: about 50% of Pb is very mobile
• calculated vertical Pb migration velocity 0.3-0.36 cm/year
Ettler et al. (2005): Chemosphere 58, 1449., Ettler et al. (2004): ABC 378, 311.
Soil pollution in Copperbelt, Zambia
• topsoils/subsurface
• maximum values
Cu 41900 ppm
Co 606 ppm
Pb 503 ppm
Zn 450 ppm
As 255 ppm
Kříbek et al. (2010) J. Geochem. Explor. 104, 69-86
Fly ash reactivity – leaching tests
• fly ash sampled at bag-house filters in the smelter
• rapid dissolution of primary phases
• pH-dependent
release
• relevant for
soil systems
Ettler et al. (2008) ES&T 42, 7878.
Vítková et al. (2009) J. Hazard. Mater. 167, 427.
pH-stat
Incubation of fly ash in soils
• 0.5 g fly ash
• sealed by welding
• testing bags – polyamide
fabric (NYTREL TI)
• mesh size 1 μm
• double bags
Laboratory pot experiments
60% WHC
pore water sampling in time
Metal release into soil water
• high and quick release of Cd into soil and soil water
• lower release of Pb – efficient attenuation processes
In situ experiments
• sampling of soil before
experiment
• testing bag insertion
Soils and cadmium (Cd) distribution
increase 51x
increase 250x
increase 46x
• for a given pH range mostly independent Cd release
Soils and lead (Pb) distribution
increase 1.4x
increase 3x
increase 16x
• strong pH-dependent release of Pb for given conditions
Chemical fractionation of metals
• shift towards more mobile forms after the fly ash exposure
Conclusions #2
Fate of smelter emissions in soils
• laboratory and in situ experiments help to decipher
the processes affecting fly ash reactivity in soils
• direct comparisons with polluted soils
• smelter emissions are often composed of soluble
phases
• low soil pH is accelerating the dissolution and
influences subsequent mobility of contaminants
in soil profiles
General conclusions
• smelter-affected environments are convenient
natural laboratories for understanding the dynamics
and fate of anthropogenic contaminants
• multi-method approaches needed
• knowledge of behaviour of smelter-derived
contaminants can help to innovate smelting
technologies to be more „environment-friendly“
• indications for possible ways for recycling of
smelting waste products
Thanks for your attention!
ettler@natur.cuni.cz